Variations of fin whale vocalizations in the Northeast Pacific and the effects of environmental parameters on acoustic sensitivity

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[author abstract] Declines in fin whale populations have instigated significant interest regarding their life history, feeding patterns, mating habits, and migration. Our current lack of understanding could be remediated by the use of passive acoustic methods to examine vocalization patterns. Data from seismometers and hydrophones exclusively associated with cabled observatories have been analyzed to monitor vocalization changes with distance from shore and between normal (2014-5) and El Niño Southern Oscillation (ENSO; 2015-6) years. Tens of thousands of calls were resolved, with a total of 3.6*105. During ENSO relative to the normal season, there was a decrease in overall vocalizations along with a regional shift both onshore and southward. Additionally, as exhibited in both seasons, vocalization patterns occurred later in time at offshore instruments relative to those onshore. This time lag was more pronounced at higher latitudes. Different instruments and environments allowed for a quantified analysis of sensitivity as both instrument specifications and environmental parameters fluctuated. Sensitivity was found to linearly increase with depth by ~0.03% m-1. Seismometers atop basalt were 2x as sensitive as those on sediment. Seismometers on basalt exhibited ~78% the sensitivity of hydrophones; those on sediment exhibited ~38% sensitivity. According to these changes in sensitivity, the use of weighted data was proposed based on ecological and instrumental characteristics.